This invention relates generally to rotor shaft assemblies, and more particularly, to a method of assembling a rotor shaft assembly.
Generally, a wind turbine generator includes a rotor having multiple blades. The rotor is sometimes mounted within a housing, or nacelle, that is positioned on top of a base, for example a truss or tubular tower. At least some known utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have rotor blades of 30 meters (m) (100 feet (ft)) or more in length and include a mechanical drive train. The drive train extends from the blades to a generator positioned within the wind turbine. As wind encounters the blades, the blades rotate, thus causing the mechanical drive train to rotate. By rotating, the drive train transfers wind energy to the generator. To efficiently transfer wind energy to the generator, the drive train should remain stationary, horizontally and vertically, while rotating. A main bearing is positioned at a blade/drive train interface and defines a location that allows the drive train to rotate while preventing the drive train from moving horizontally and vertically.
During operation, wind loading at different areas of the blades may be different and may cause the blades to bend. Because the blades are connected to the drive train, bending of the blades may cause angular misalignment, or bending, of the drive train. Consequently, known main bearings may generally be provided to accommodate angular misalignment of the drive train.
Known main bearings generally include spherical roller bearings (SRBs) to accommodate misalignment of the drive train. SRBs may provide an indeterminate force balance and also may inherently provide radial and axial bearing clearances. These radial and axial bearing clearances may not be well suited for dynamic loads imposed on drive trains, so SRBs may not achieve a twenty year useful life.